1. Field of the Invention
The present invention relates generally to lasers, particularly to multi-wavelength lasers and to Interferometric Sensors that are Wavelength Division Multiplexed and utilize multi-wavelength laser sources.
2. Technical Background
To handle the explosion for data capacity in telecommunication systems, system designs are using wavelength division multiplexing (WDM) to obtain more data capacity. Thus, more laser sources of higher quality are needed to build and characterize WDM systems. A significant and growing fraction of the total cost in WDM systems is due to laser sources. Currently each WDM channel requires its own laser source. For example, a telecommunication system which is being designed for eighty wavelengths operation will need eighty source lasers. Future systems will be requiring even more laser wavelengths as the systems expand. Large cost savings can be realized by developing cheaper laser sources. The telecommunication systems as well as the test and measurement systems for WDM systems will realize the cost savings due to cheaper laser sources.
One way to make laser sources cheaper is to exploit the natural characteristics of Erbium Doped Fibers (EDF). The wide bandwidth of the EDF gain profile provides an ideal gain medium to design a multi-wavelength laser. The longitudinal modes of the laser cavity, which lase simultaneously at multiple wavelengths, are formed by using standard telecommunication components such as gratings, fiber Bragg gratings, thin films, phasors, and liquid crystal devices. Erbium Doped Fiber Laser (EDFL) wavelengths can be easily added or dropped. It is desired that an improved EDFL will be able to provide the necessary laser wavelengths to cover the ITU grid or any desired subset.
The need for cheaper lasers transcends the telecommunication industry. As more efficient designs of complex systems involving engineering structures, adaptive structures and manufacturing processes evolve, the ultimate limits of the engineering materials used in the systems are being approached. The reduced margins of safety for the materials used in the design of the complex systems will require the use of sensing systems to measure displacements, strain and temperature at a number of critical locations. These measurements will allow the designs to maintain safety and reliability.
Traditional electronic based sensors such as strain gauges, thermocouples, and resistive displacement sensors work well for applications which require only a relatively small number of sensors. To build large sensing arrays from electrical based sensors, the designer would be required to use complex routing, elaborate harnessing and delicate switching schemes. The additional wiring and electronics would interfere with the functionality of the structure even if state of the art thin film or MEMS sensors are used.
Optical sensors can reduce the complexity and the amount of routing because the interferometric sensors are non-contacting and can be WDM. Therefore, the optical sensor does not need to be mounted to the test specimen. Since the interferometric sensors can be WDMed or otherwise multiplexed, a single transmission fiber can send/receive light to/from multiple transducers. The multi-wavelength laser provides for the efficient generation and transmission of the optical energy to interrogate the optical sensors.
One aspect of the present invention is the generation of a laser synthesizer. A multi-wavelength laser includes an optical loop having a plurality longitudinal modes and a wavelength selector insertable into the optical loop for selecting at least one particular longitudinal mode from the plurality of modes for synthesizing desired laser wavelengths.
In another aspect, the present invention includes a wavelength division multiplexor as the wavelength selector.
Yet another aspect of the present invention is the construction of WDM interferometric sensors which efficiently utilize the multi-wavelength laser source.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.